Process of purifying pig-iron



(No' Model.)

J. P. WITHEROW.

PROCESS OF PURIFYING PIG IRON. No. 314,504. Patented Mar; 24, 1885.

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JAMES P. VITHEBOW', OF ALLEGHENY, PENNSYLVANIA.

PROQES$ OF PURlFYlNG PlG-ERON.

@PECIFECATION forming part of Letters Patent No. 314-,50t, dated iviarch 2%, 1855.

Application filed January 16, 183 1, (No moth-Ll To all whom it may concern:

Be it known that I, J AMES Pon'rnn WITH- EROW, of Allegheny city, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in the Manufacture of Iron and Steel; and I do hereby declare the following to be a full, clear, and exact description thereof.

My invention relates to an improved process of purifying pig-iron in a converter, open-hearth, or other furnace in which apneu matic blast is used as the agent for eitecting the conversion of pig iron into steel or wroughtiron; and it consists in tapping off the slag during the blow and at or about the instant dissociation of the impurities takes place, whereby there is removed. with the slag the deleterious components of the pig-iron.

In the Bessemer or pneumatic process as practiced by me the silicon of the pig metal is first eliminated by means of the slag, which is formed by the combination of oxide of iron and silicic acid, and this slag is removed as formed during the early stages of the blow and without interrupting it. The oxidation and elimination of the carbon is next accomplished, and if phosphorus be present in the metal it may be removed by the further oxidation of the metal, or by adding oxides and removing the resultant slag before the phosphorus has an opportunity to recombine with the metal,- as hereinafter stated.

It is evident that the process is applicable to use with metal containing either phosphorus or sulphur, or both. These metalloids aid in keeping up the heat of the bath after the elimination of the silicon and carbon, which is of importance in maintaining the bath in the ex tremely liquid condition which is essential to the successful operation of the process. These conditions are more readily, rapidly, and perfcctly obtained by raising the temperature of the blast, which may be done by means of a heating or superheatiug stove. The use of a heated or superheated blast serves, moreover, to import into the converter or furnaccalarge amount of heat in addition to that which is developed by the fuel contained in the metal itself, and thus increase the calorific power of the blast and accelerate and intensify the reactions in the converter.

To enable others skilled in the art to make and use my invention, I will now describe it by reference to the accompanying drawing, which is a view of a converter-plant having a super-heating blast apparatus, a portion of the view being in section.

Here A indicates a blowing-engine of any suitable construction, for the purpose of pumping and forcing atmospheric air into the converter to effect the operations and reactions therein.

B indicates a Whitwell fire-brick or superhcating stove, to which the blast passes. from the engine by pipes a a, and in which the air may be heated.

(2 indicates a fixed converter, having ablastmain, (1, blast-pipes d, tuyeres c, charginghole,f, a slag-tapping hole, 9, situated at or slightly above the metal line, and a tappinghole, 71. The blast-trunk (Z is connected with the heating-stove B by pipes b. The charg ing-hoie is connected with the cupola F by a spout, f.

Thus constructed and arranged the converter may be operated in the usual way, except that the slag is tapped off through the slag-hole g at or about that period of the blow when the dissociation of the impurities of the metal is more or less complete, and before they begin to reunite with the metal. The slag with the impurities is thus removed from the converter during the earlier stages of the blow, and without interrupting it. As the impurities are thus removed from the converter they cannot recombine with the iron at any subsequent stage of the process. At this period the slag is in a light foamy condition, and being of less specific gravity than the metal it floats on top of the latter, so that it can be removed. from the converter without tapping the metal. Thisis accomplished in the converter 0 through the slagging-hole g, which, being on or nearly on a level with the metal line, will, it opened, permit the slag to flow out, especiallyin view of the fact that the effect of the blow and the intensely-agitated condition of the highlyfluid slag and its character causes the latter to swell and boil or flow over through the slagging-hole g, particularly at the period of practically complete dissociation of the iron and its impurities.

The object of the immediate and successive removals of slag from the bath, as described,

is to prevent the injurious effects resulting from the continued contact of the same with the metali'or example, if the phosphorus is carried to the slag in the form of phosphates and allowed to remain on the surface of the bath, it would recombine with the metal, ow-

ing to the action of the reducing gases formed by the blast passing through the charge. Furthermore, the phosphates may be reduced by the presence of free silicic acid, and for this reason, if the phosphorus is to be removed, it is desirable to remove the slag containing the silica during the earlier stages of the blow. Should the metal become chilled orpasty, OW- ing to the lack of silicon, phosphorus, orother heat-giving agents, the fluidity of the bath may be sustained by external heat, or by the use of a heated or superheated blast, as hereinbefore described, and the use of the heated-air blast will also allow of the addition of scrap and like materials, which would otherwise chill the bath. By my process the silicon will be more rapidly and thoroughly removed and the phosphorus be less liable to return to the metal. If it is preferred to permit the phosphorus to remain in the resultantproduet, the removal ofthe slag is not repeated.

I do not herein claim the apparatus for converting pig metal into wrought-iron or steel for the reason that it forms the subj act-matter of a separate application of even date.

What I claim as my invention, and desire to secure by Letters Patent, is

l. The process of purifying a charge of molten pig metal, which consists in blowing or oxidizing the metal, as described, and removing the slag during and Without interrupting the blow, substantially as and for the purposes described.

2. The process of purifying a charge of molten pig metal, which consists in blowing or oxidizing the metal, tapping off the slag containing the silica, then continuing the blow, and subsequently tapping the slag again to remove the phosphorus, substantially as described.

3. The process of purifying a charge of molten pig metal, which consists in blowing or oxidizing the metal, removing the silicon, phosphorus, and other impurities by succes: sive discharges of slag during the continuance of the blow, and maintaining the heat, after the carbon, silicon, and phosphorus are eX- hausted, by a heated or superheated blast, substantially as and for the purposes described.

In testimony whereof I have hereunto set my hand this 4th day of January. A. D. 1884. JAMES P. NVITHEROWV.

Witnesses:

W. B. OoRwIN, THOMAS B. KERR. 

